Sakura from Naruto.
I have a love/hate relationship with her. In the first part she was annoying and useless. In Shippuden, I came to respect her new found strength and power, but I still have a problem with some of the actions she makes, haha. In either case, I don't think she's useless as she use to be anymore, despite a lot of people still believing she is.

Usopp and Rock Lee are probably my two biggest changes of opinion. The character designs on both were so aggravating to me that I despised them on principle especially as they are both originally presented as complete goobers only existing for juvenile comic relief. However my opinion of both characters did a 180 fairly shortly as they show themselves to be some of the most admirable characters(and my personal respective favorites) in their shows. Just goes to show that appearances aren't everything.

I never like the haughty emotionless girls at first. I only start to like them after their respective animes try really hard for me to do so. The three I can think of are Senjougahara from Bakemonogatari, Masuzu from Oreshura, and Aika from Blast of Tempest.

Out of the three, Senjougahara easily wins. I still haven't finalized my opinions on the other two.

EDIT: I remember what I was looking for now. TEASES. I can't stand teases lol. Holo is another example of a tease that the anime goes to great lengths to make sure you understand that she has a good personality, darn it. (Holo is pretty cool, though)